This application is based upon and claims the benefit of priority from the prior Japanese Patent Application No. 2000-376947, filed on Dec. 12, 2000, the entire contents of which are incorporated herein by reference.
The present invention relates to a high pressure discharge lamp which is provided with a light-transmissive ceramic discharge vessel, a high pressure discharge lamp lighting circuit, and a luminaire therefor.
A compact metal halide type high pressure discharge using a light-transmissive ceramics with a rated lamp power of about 20 W is described in co-pending Japanese Patent Application No. 2000-6994, which has been devised by the inventors of the present invention and filed Jan. 14, 2000 (hereinafter referred to as 6994 Prior Application).
The 6994 Prior Application refers to a high pressure discharge lamp having a light-transmissive ceramic discharge vessel which is provided with an enclosure defining a main discharge space and a pair of thin cylindrical portions integrated with both ends of the enclosure. A feed-conductor and an electrode which is mounted on the end of the feed-conductor are inserted in the slender thin cylindrical portions of the light-transmissive ceramic discharge vessel, and the thin cylindrical portion and the feed-conductor are sealed by using a ceramic sealing compound, which is the so-called a frit glass. A discharge agent comprised of a luminous metal halide, mercury, and rare gas is filled in the light-transmissive ceramic discharge vessel.
On the other hand, as such sealing configurations other than that as mentioned above, a high pressure discharge lamp wherein a sealing body which is made of cermet and a metal pipe acting as a current conductor are mounted on the end of a ceramic discharge tube (light-transmissive ceramic discharge vessel) has been disclosed in the Japanese Laid-Open Patent Application Hei 8-250068 (hereinafter referred to as Prior Art I). Moreover, a high pressure discharge lamp wherein a metal rod is inserted in such a metal pipe has been disclosed in the Japanese Laid-Open Patent Application Hei 10-334852 (hereinafter referred to as Prior Art II). Then, the metal pipe itself is fused to seal the ceramic discharge tube.
The Prior Art II discloses that when the high pressure discharge lamp disclosed in the Prior Art I is applied to the metal halide lamp, a metal rod is inserted in the metal pipe in order to reduce conductance inside of the metal pipe, so as to prevent some problems such as a reduction in luminous efficiency by the metal halogen flocculating in the metal pipe which becomes the lowest temperature portion during the operation of the lamp.
Further, a technique to fuse both of a metal lead to which an electrode rod is connected and the metal pipe by heat is shown in FIGS. 9 and 10 of the EP 982278A1 (hereinafter referred to as Prior Art Ill). Furthermore, it is disclosed that it has a coupling configuration which a first member made of ceramics or cermet and a second member made of a metal are connected together by interposing a main phase that contacts with the first member and an intermediate glass member that contact with the second member. Here, the intermediate glass member, that contact with the second member, is interposing between the second member and the main phase that has a porous skeleton configuration made from a sintered metal powders with an opening to which a glass phase is sunk.
Furthermore, a metal halide lamp wherein two ends of a light-transmissive ceramic arc tube are closed by ceramic plugs, through the ceramic plugs molybdenium exhaust pipes are fused, and electrode core rods are welded to inner ends of the ceramic plugs, is described in the Japanese Laid-Open Patent Application Hei 10-284004 (hereinafter referred to as Prior Art IV).
Furthermore, a technique to fuse by heat both of a metal lead to which an electrode rod is connected and the metal pipe is disclosed in FIGS. 9 and 10 of the EP 982278A1 (hereinafter referred to as Prior Art III).
In the high pressure discharge lamp discussed in the 6994 Prior Application, since the thin cylindrical portion becomes relatively longer in comparison to the enclosure, dead spaces tend to become broader in case of miniaturization.
On the contrary, the high pressure discharge lamps disclosed in the Prior Arts I, II and III are suitable for miniaturization in a point that it does not need a longer thin cylindrical portion. However, these Prior Arts do not mention to a relation between the luminous efficiency as a metal halide lamp, the lowest temperature portion to determine the luminous color and a sealing configuration.
That is the Prior Arts I-III are not able to rise the temperature of the lowest temperature portion by using w fusing configuration.
Under the circumstances, as a result of a meticulous research for such sealing configurations using a metal pipe, the inventors of the present invention have accomplished the present invention.
As a result of the research, it was proved that the Prior Arts I and II ware much the same. That is, in the high pressure discharge lamp disclosed in the Prior Art II, since the electrode is shorter than the metal pipe, there is left a gap, which becomes a capacity permitting aggregation of metal halide inside of the metal pipe. Then, if the electrode is extended in the metal pipe, the same effect as the case or the Prior Art II that the metal rode is inserted in the metal pipe is achieved.
Further, it is not mentioned about the causes or conditions for forming the lowest temperature portion in the metal pipe in the Prior Art II. According to the studies of the inventors, it was found that even in the high pressure discharge lamp disclosed in the Prior Art II, the lowest temperature portion might to be formed in the enclosure depending on the size of the light-transmissive ceramic discharge vessel and the metal pipe. Thus, it is proved that the techniques disclosed in the Prior Arts do not always achieve enough luminous efficiency, but also not suppress the difference of the luminous color at the time of changing the lighting direction.
Furthermore, the Prior Art IV is different from the present invention by that the Prior Art IV has a configuration of sealing the arc tube made of light-transmissive ceramics by a ceramic plug. The Prior Art IV is also different from the present invention in the inventive subject by that the Prior Art IV is subjected for preventing cracks of molybdenium exhaust pipe passing through the ceramic plug. On the other hand, the present invention is subjected for achieving a high luminous efficiency by raising a lowest temperature portion as described later. The Prior Art IV also has a problem that the exhaust pipe cannot be thickened because that the electrode is welded to a part of the inner wall of the exhaust pipe and thus placed eccentric from the axis of the arc tube.
The present invention has an object to improve the light-transmissive ceramic discharge vessel and the sealing configuration for providing a high pressure discharge lamp, high pressure discharge lamp lighting device, and a luminaire, which have an excellent luminous efficiency and/or a desired luminous color, and also, albeit compact, suppress the difference of the luminous color due to lighting directivity.
Further, the present invention has another object to provide a high pressure discharge lamp, a high pressure discharge lamp lighting device, and a luminaire which have longer life-expectancy.
A high pressure discharge lamp according to the first aspect of the invention is comprised of a light-transmissive ceramic discharge vessel with an envelope having a maximum outer diameter D1 and open ends, a metal pipe disposed in each or the open ends, respectively each metal pipe having a first end, i.e., a top end fused, located in one of the open ends of the light-transmissive ceramic discharge vessel and a second end, i.e., a base end protruding from the light-transmissive ceramic discharge vessel, a plurality of electrodes each having a first end, i.e., a base end connectively supported on the base end connected to a corresponding metal pipe and a second end, i.e., a top end extending within the light-transmissive ceramic discharge vessel, and a discharge agent which is filled in the light-transmissive ceramic discharge vessel, wherein it is also characterized by that the high pressure discharge lamp has an overall length L1, and the overall length L1 and the maximum outer diameter of D1 satisfy a following equation.
xe2x80x831.5xe2x89xa6L1/D1xe2x89xa64.5
In the high pressure discharge lamp according to the first aspect of the invention, since it defines the ratio L1/D1 of the maximum diameter D1 of the enclosure of the light-transmissive ceramic discharge vessel to the overall length L1 of the high pressure discharge lamp in a range from 1.5 to 4.5, it is able to define the temperature of the lowest temperature portion high, so as to achieve the high luminous efficiency and/or a desired luminous color. Further, since the temperature of whole high pressure discharge lamp is comparatively equalized, the temperature of the lowest temperature portion does not change a lot even when the lighting direction of the high pressure discharge lamp is changed from a horizontal to downward, so that the difference of the luminous color is decreased.
On the contrary, if the ration L1/D1 is less than 1.5, the distance between a hot positive column and the wall of the enclosure of the light-transmissive ceramic discharge vessel is expanded. Thus, the lowest temperature portion is easily formed in the enclosure, and the temperature of the lowest temperature portion lowers, so that the luminous efficiency and the lighting color change are increased. In addition, since an excessive discharge agent coagulates in a liquid-phase in the lower portion of the enclosure which is used as the lowest temperature portion during the horizontal lighting operation, and casts a shadow on light radiating surface, the light distribution is deteriorated. Thus this case is unfavorable.
On the other hand, if the ratio L1/D1 is higher than 4.5, the lowest temperature portion is easily formed in the metal pipe, and the temperature lowers. Then, the luminous efficiency also lowers, and the luminous color change increases. Thus this case is also unfavorable.
The tendency mentioned above could be thought that the portion where the lowest temperature portion is formed and its temperature depend on the distance from the positive column, the heat capacity of whole high pressure discharge lamp, and the balance of the bulb wall load, after all, they depend on the ratio L1/D1, since the light-transmissive ceramics that is a components of the discharge vessel has a better thermal conduction than a silica glass, and the metal pipe has also excellent thermal conduction. The operations and effects mentioned above do not change in any lighting method of the high pressure discharge lamp, for instance, they do not change even though the lighting frequency is high of 45 kHz or it is low of 50 Hz. Furthermore, they do not change even it is an AC lighting or DC lighting. Moreover, it shows the same tendency even when the bulb-wall loads are any within the range of at least 10 to about 45 W/cm2.
The high pressure discharge lamp according to the second aspect of the invention is characterized by that, further to the high pressure discharge lamp according to the first aspect of the invention, the overall length L1 of the discharge lamp is less than 30 mm.
This aspect of the present invention defines the overall length of the high pressure discharge lamp in the range mentioned above. When the overall length is within the range, it is able to achieve an effect to define the ratio L1/D1 in the first aspect of the invention remarkably.
The high pressure discharge lamp according to the third aspect of the present invention, comprising a light-transmissive ceramic discharge vessel with an envelope and open ends, a metal pipe having one end, i.e., a top end fused in the open end of the light-transmissive ceramic discharge vessel and the other end, i.e., a base end protruding from the light-transmissive ceramic discharge vessel, a pair of electrodes each having one end, i.e., a base end connectively supported on the base end of the metal pipe and the other end, i.e., a top end extending within the light-transmissive ceramic discharge vessel, a discharge agent which is filled in the light-transmissive ceramic discharge vessel, and wherein the overall length L1 of the discharge lamp is less than 30 mm, and the temperature difference between the highest temperature portion and the lowest temperature portion is less than 400 degrees during the operation of the lamp.
Here, when sealing the light-transmissive ceramic discharge vessel using a frit glass, i.e., a ceramic sealing compound, if the frit glass, e.g., a composed of SiO2xe2x80x94Al2O3xe2x80x94Dy2O3, is not kept below 700 degree, leaks become remarkable during the life of the discharge lamp. This is because the lowest temperature portion is formed near the frit glass portion and these temperatures are linked each other. If the temperature of the flit glass portion lowers, the temperature of the lowest temperature portion will also lower, and also the luminous efficiency will lowers with the temperature lowering of the lowest temperature portion.
On the other hand, the maximum operation temperature of the light-transmissive ceramic discharge vessel is about 1200 decree when the light-transmissive ceramics is made of alumina. If it is more than 1300 degree, it would cause sublimation or crack, so that it is impossible to achieve sufficient life characteristic. Therefore, in designing the high pressure discharge lamp, it is necessary to take into consideration the balance of two matters mentioned above. In summary, in a configuration as discussed in the 6994 Prior Application, the lowest temperature portion will be 700 degree, and the highest temperature portion will be 1200 degree. It is necessary to form the difference about 500 degree between them.
However, in a compact high pressure discharge lamp having the overall length of less than 30 mm and lamp power of about 20 W, it was difficult to make the temperature difference mentioned above. That is, since the light-transmissive ceramics has an extremely better thermal conduction rate than the silica glass, it is hard to make the temperature difference in a material level. Further, when the operation temperature of the light-transmissive ceramics discharge vessel is tried to be controlled by the shape of the enclosure or the length of the thin cylindrical portion, it causes a drawback such as lowering the ratio of the light-emitting portion to the high pressure discharge lamp in size, in other words, enlarging a dead space. As a result, the luminous efficiency is also lowered. Further, if the temperature difference becomes wide, the thermal stress of each portion will be enhanced. When things come to worst, the crack might occur.
On the contrary, in a high pressure discharge lamp according to the third aspect of the invention, the electrode is coupled to the high pressure discharge lamp by using a metal pipe which seals the light-transmissive ceramic discharge vessel, and its overall length is less than 30 mm. Further, since it defines the temperature difference between the highest temperature portion and the lowest temperature portion during the operation of the lamp less than 400 degree, it is able to define the lowest temperature portion higher than the case of using the frit glass for it. Therefore, the luminous efficiency is enhanced, and the temperature difference in the light-transmissive ceramics discharge vessel lowers, so as to lower the possibility to cause the crack.
In addition, in this third aspect of the invention, the temperatures of the highest portion and the lowest temperature portion is achieved by measuring the temperature of the outer portion of the high pressure discharge lamp by using a radiation thermometer.
In this aspect of the invention, the electrodes are connectively supported on the sealing portions of the base ends of the metal pipes. Accordingly, it is possible to simultaneously execute the fusing between the electrodes and the base ends of the metal pipes and the supporting of the electrodes. For example, the simultaneous execution of the fusing between the electrodes and the base ends of the metal pipes and the supporting of the electrodes can be made by previously fixing the fusing metal for fusing the metal pipe on the base end of the electrode, then placing the electrode in the light-transmissive ceramic discharge vessel and then melting the fusing metal by heat.
The high pressure discharge lamp according to the forth aspect of the present invention, comprising a light-transmissive ceramic discharge vessel with an envelope and open ends, a metal pipe made of a metal having a melting point of T1, whose one end, i.e., a top end is fused in the open end of the light-transmissive ceramic discharge vessel and whose other end, i.e., a base end is protruding from the light-transmissive ceramic discharge vessel, a fusing metal, made of a metal having a melting point of T2, which seals the base end of the metal pipe, a pair of electrodes each having one end, i.e., a base end connectively supported on the base end of the metal pipe via fusing metal and the other end, i.e., a top end extending within the light-transmissive ceramic discharge vessel, and a discharge agent which is filled in the light-transmissive ceramic discharge vessel, wherein it is characterized by that the melting point of T1 of the metal pipe and the melting point of T2 of the fusing metal satisfy a following equation.
T1 greater than T2
The present invention provides a suitable configuration for sealing the metal lamp and coupling the electrode to the metal pipe. That is, the base end of the metal pipe is sealed by the fusing metal. When the relation between the melting point T1 of the metal pipe and the melting point T2 of the fusing metal satisfies the condition shown by the above-mentioned equation, it is able to perform the fusing splicing of the fusing metal to the metal pipe easily and certainly. Accordingly, the length of top end of the metal pipe protruding in the enclosure is shorten as much as possible, and it is possible to prevent the decrease of the strength of sealing the ends of the light-transmissive ceramic discharge vessel, e.g., the sealing of the thin cylindrical portion, the metal pipe, and the light-transmissive ceramic discharge vessel at the time of sealing the metal pipe by using the fusing metal, and it is also prevent causing the crack. Here, it is more preferable that the melting point T1 of the metal pipe and the melting point T2 of the fusing metal satisfy a relation given by an equation; T1xe2x88x92T2xe2x89xa7500xc2x0 C. That is, when the metal pipe is made of molybdenum or tungsten, it is preferable to be made of platinum or molybdenum.
To seal the base end of the metal pipe by using the fusing metal, a proper lump of the fusing metal is put on the opened end of the metal pipe, then the fusing metal is heated by the laser-beam irradiation etc. Thus, since the perimeter of the lump of the fusing metal will be fused to the opened end of the metal pipe, so that the metal pipe is sealed.
On the other hand, the electrode is supported by coupled to the metal pipe by using the fusing metal. That is, the electrode is coupled to the metal pipe via the fusing metal wherein the base end of it is buried. Thus it is supported by one side by the metal pipe. To achieve the high pressure discharge lamp having the configurations mentioned above,
For instance, the metal pipe is sealed to the thin cylindrical portion of the light-transmissive ceramic enclosure, next, the lump of the fusing metal is adhered on the basic end of the electrode, then the electrode is inserted vertically inside of the metal pipe through the opened base end of it. Then, in the state that the lump of the fusing metal is located on the opened end of the base end of the metal pipe, the fusing metal is heated to be fused by the laser-beam irradiation etc. Here, by performing the operations mentioned above in an atmosphere of an ambient gas, it is able to prevent the oxidization of the metal, so that the fusing splicing of the fusing metal to the metal pipe is performed certainly and the discharge agent is filled in the enclosure easily.
Thus, according to the present invention, sealing the metal pipe and coupling the electrode to the metal pipe will be easy, so that it will be easy to manufacture the high pressure discharge lamp.
The high pressure discharge lamp according to the fifth aspect of the present invention is characterized by that further to the high pressure discharge lamp according to the fourth aspect of the invention, when the length of the electrode is L3, and the length L4 of the fusing metal in the bulb axis direction, it satisfies a following equation.
L3 greater than L4
In this fifth aspect of the invention, the length of the fusing metal L4 is defined by comparing to the length L3 of the electrode. That is, within the range satisfying the equation mentioned above, the length of the fusing metal does not have an adverse effect to support the electrode. However, if the length L4 of the fusing metal exceeds the length L3 of electrode, it will easy to cause the electrode off-centered from the bulb axis according to the deformation of the fusing metal at the time of fusing the fusing metal, or it will also easy to cause the dispersion of the electrodes according to the undesirable change of the distance between electrodes. Further, if the fusing metal is long, its reaction to the erosion causes a blackening, and it might to cause a trouble to a life characteristic.
In this fifth aspect of the invention, the length L3 of the electrode is the portion exposed from the fusing metal even though its base end is buried in the fusing metal.
The high pressure discharge lamp according to the sixth aspect of the invention, is characterized by that, further to the high pressure discharge lamp according to any one of the first to fifth aspects of the invention, a light-transmissive ceramic discharge vessel is provided with a thin cylindrical portion with an outer diameter D2 formed at the end of the enclosure, and a metal pipe with outside diameter D3 which is inserted in a thin cylindrical portion of the light-transmissive ceramic discharge vessel for closing the end of the light-transmissive ceramic discharge vessel, wherein the ratio of the outer diameter D2 of the thin cylindrical portion and the outer diameter D3 of the metal pipe satisfies a following equation.
1.5xe2x89xa6D2/D3xe2x89xa64.0
The thin cylindrical portion is generally formed at the both ends of the enclosure of the light-transmissive ceramic discharge vessel. If needed, a pair of the thin cylindrical portions may be formed at one end of the enclosure, or a single but large sized thin cylindrical portion may be formed.
The top end of the metal pipe is inserted into the thin cylindrical portion and sealed thereto via a sealing layer which is primarily made of, e.g., a cermet. Here, the cermet is a composite material of ceramics powder and metal powder which are pressed and sintered, and it includes a heat-resistant of the ceramics and a toughness of the metal. As the ceramics, it is able to use a ceramics which is same as or similar to the light-transmissive ceramics. Further as the metal, it is able to use the same metal as the metal pipe or an alloy having the similar characteristics as the metal pipe.
Therefore, when interposing a sealing layer which is primarily made of a cermet between the thin cylindrical portion and the metal pipe, an inclination configuration is formed between them, so as to achieve a suitable sealing. Further, the above mentioned composite configuration which is disclosed in the Prior Art III is able to be adapted to the sealing layer. In addition, if needed, the outside of the sealing layer is covered with a sealant of a ceramic sealing compound at the end of the thin cylindrical portion. Accordingly, the sealing of the thin cylindrical portion and the metal pipe is reinforced, so that the hermetically reliability is enhanced all the more.
Furthermore, the present invention defines a suitable condition between the outer diameter of the thin cylindrical portion D2 and the outer diameter of the metal pipe D3. That is, within the range mentioned above, it does not cause the crack on the thin cylindrical portion, even though the thermal stress is generated by the temperature change at the time of blinking during the operation of sealing and lighting. On the other hand, if the ratio D2/D3 is less than 1.5, the thickness of the thin cylindrical portion becomes thinner than that of the metal pipe, therefore the mechanical strength is insufficient, so that it will be easy to cause the crack on the light-transmissive ceramic discharge vessel by thermal stress that occurs according to the temperature change during the operation of sealing of the thin cylindrical portion and the metal pipe or the time of blinking.
Furthermore, if the ration D2/D3 exceeds 4.0, the thickness of the thin cylindrical portion becomes relatively thick, therefore the temperature gradient between the inner surface and the outer surface of the thin cylindrical portion is increased during the operation of the sealing or at the starting operation. Accordingly, the thermal stress generated in such cases exceeds the maximal acceptable strength of the light-transmissive ceramic discharge vessel, whereon the crack will be easily caused.
A high pressure discharge lamp according to the seventh aspect of the invention, is characterized by that further to the high pressure discharge lamp according to any one of the first to sixth aspects of the invention, the electrode, whose overall length L3 is equal to or longer than 4 mm, is comprised of an electrode base-rod having a diameter D4 of less than 0.3 mm, and an electrode principal portion which is placed at the end of the electrode base-rod.
In a configuration wherein the metal pipe is used for sealing the light-transmissive ceramic discharge vessel and for supporting the electrode also, not only the electrode and metal pipe, but a feeder lead coupled to the metal pipe works as an electrode while the glow-arc transition. Taking this into consideration, the electrode needs to be constituted appropriately.
However, if the electrode is constituted inappropriately, the glow-arc transition time becomes longer, it might to cause a blackening due to a spattering of the metal pipe or the electrode by the ion impact in a glow discharge or a leak due to the consumption of the metal pipe. According to the studies by the inventor of the present invention, the cause of extending the time of the glow-arc transition is assumed to be increased amount of the thermal conduction from the electrode to the metal pipe. That is, in a glow discharge until around the tip end of the electrode reaches to a glow-arc transition temperature and migrates to an arc discharge, the heat is easily conducted excessively from the electrode to the metal pipe.
In the present invention, since it is provided with the configuration mentioned above, it is able to reduce the thermal conduction quantity during the glow discharge, so that the glow-arc transition time is hard to be extended.
The high pressure discharge lamp according to the eighth aspect of the present invention, is characterized by that further to the high pressure discharge lamp according to any one of the first to seventh aspects of the invention, the metal pipe satisfies a following equation with its length L2 (mm) that is exposed outside the light-transmissive ceramic discharge vessel.
1.0xe2x89xa6L2xe2x89xa64.0
The eighth aspect of the present invention reduces as short as possible the a portion of the metal pipe exposed outside the light-transmissive ceramic discharge vessel to miniaturize the high pressure discharge lamp, and limits the length L2 of the metal pipe exposed outside the light-transmissive ceramic discharge vessel in the range given in the above equation. Therefore, it is able to prevent the decrease of the strength at the ends of the light-transmissive ceramic discharge vessel, e.g., the thin cylindrical portions themselves, or the sealing layer for sealing the metal pipe due to the thermal shock caused at the time of sealing the metal pipe.
On the contrary, if the length L2 is less than 1 mm, it causes the decrease of the strength at the end of the light-transmissive ceramic discharge vessel, e.g., the thin cylindrical portion itself or the sealing layer for sealing the metal pipe. If things come to worst, the cracks occur on the light-transmissive ceramic discharge vessel, or the sealing layer is felt off. Further, if the length L2 is more than 4 mm, the lowest temperature portion is easy to be formed in the metal pipe, so that the luminous efficiency is easily lowered. In addition, the overall length of the high pressure discharge lamp is enlarged, and the dead space is increased, so that it causes a trouble for miniaturization.
A high pressure discharge lamp according to the ninth aspect of the invention is characterized by that, further to the high pressure discharge lamp according to any one of the first to eighth aspects of the invention, its linear transmittance of the enclosure is set to at least 30% or more.
A high pressure discharge lamp according to the ninth aspect of the invention defines a configuration wherein its light condensing efficiency is enhanced further. That is, if the linear transmittance of the enclosure is set to 30% or more, arc""s scale effect between electrodes will arise, so that it is able to achieve a high light condense. Thus, the higher linear transmittance is able to be achieved by using e.g., YAG as a light-transmissive ceramics.
Therefore, according to the ninth aspect of the invention, it is able to achieve an still further concentrated point-source featured high pressure discharge lamp, and for instance, it is suitable for a light source for optical fibers.
On the contrary, the linear transmittance of the light-transmissive alumina ceramic is about 15%. Even though 20% of its linear transmittance could be achieved by ground, it still has an effect of a scattered light, so that it is hard to achieve high light condensing.
A high pressure discharge lamp according to the tenth aspect of the invention, is characterized by that, further to the high pressure discharge lamp according to any one of the first to ninth aspects of the invention, a pair of electrodes is asymmetrical whereof one is relatively a thick rod, and the other one is a thin rod.
This tenth aspect of the invention defines a high pressure discharge lamp provided with an electrode configuration which is suitable for DC lighting. That is, in case of DC lighting, since a positive pole is heated to a high temperature in order that a large amount of current flow through there due to flowing electrons, it is common to enlarge an anode compared with a negative pole. A conventional high pressure discharge lamp adopts a configuration to put a positive pole principal portion having a big diameter at the tip end of the electrode base-rod. However, in a case of a compact high pressure discharge lamp having the lamp power of about 20 W and the overall length L1 of about 30 mm, the electrode is relatively short, so that it becomes hard to provide asymmetrical pair of electrodes.
Thus, in the present invention, both of the positive and negative poles are formed with rods with relatively different diameters. That is, the relatively thick road is used for the positive pole of the electrodes, and relatively thin rod is used for the negative pole, so as to perform DC lighting. In DC lighting, a high-pressure chopper or a step-up chopper is able to be used for a lighting circuit, and thus it is able to simplify a circuit arrangement and miniaturize it, compared with AC lighting.
A high pressure discharge lamp according to the eleventh aspect of the invention, is characterized by that further to the high pressure discharge lamp according to any one of the first to tenth aspects of the invention, it is provided with a feeder lead having a cross-sectional area narrower than the overall cross-sectional area of the metal pipe and lead out from the metal pipe.
The eleventh aspect of the invention provide a configuration for decreasing as low as possible a thermal influence of the feeder lead for feeding the electrode against the metal pipe.
The inventors of the present invention have learned from studies that when the feeder lead is coupled to the metal pipe both of them are thermally conducted, then the heat of the metal pipe decreases by transferring to the feeder lead, thus the luminous efficiency of the high pressure discharge lamp decreases. Hence, the inventors have devised the present invention through various developments. That is, by adopting the above aspect of the invention, the heat quantity transferring from the metal pipe to the feeder lead relatively lowers, and thus it is able to achieve a high luminous efficiency and/or a desired luminous color by keeping the metal pipe in a desired temperature. Here, the term xe2x80x9coverall cross-sectional areaxe2x80x9d means a cross-sectional area of an interior defined by the outer shape of the metal pipe. Thus, it is not directly related to the wall thickness of the metal pipe. However, when considering that the metal pipe is acted upon by the internal pressure of the discharge vessel, and thus as a matter of course the metal pipe has a wall thickness enough to endure the internal pressure, it is understood that the overall cross-sectional area has a value proportional to the cross-sectional area of the wall portion of the metal pipe.
A high pressure discharge lamp according to the twelfth aspect of the invention, is characterized by that further to the high pressure discharge lamp according to any one of the first to eleventh aspects of the invention, it is provided with a heat insulator which covers the outer surface of the portion of the metal pipe exposed outside the end portion of the light-transmissive ceramic discharge vessel.
The heat insulator may be any material, if it is a material with a thermal conductivity lower than that of the metal pipe. However, it is desirable to use a compression molding of metallic oxide particles or metallic particles or a coating film primarily comprised of metallic oxide particles. Further, though it is not limited but preferable that the heat insulator entirely covers the exposed portion of the metal pipe. That is, it is essential that the insulator covers a principal portion of metal pipe. Therefore, a part of the metal pipe is left exposed without being covered by heat insulator.
Though it is able to keep the temperature of the lowest temperature portion high so as to achieve the high luminous efficiency and/or a desired luminous color by closing the ends of the light-transmissive ceramic discharge vessel with a metal pipe and defining the relation of the overall length L1 of the high pressure discharge lamp and the temperature difference of the highest temperature and the lowest temperature portion, or the relation of the melting point T1 of the metal pipe and the melting point T2 of the fusing metal within a prescribed region, if it is able to further rise the temperature of the metal pipe by a heat insulator it is more favorable for the luminous efficiency and the luminous color.
Therefore, in this embodiment it is able to restrict the temperature lowering of the metal pipe due to the heat dissipation, and thus it is able top keep lowest temperature portion in still higher temperature. As a result, it is able to keep the luminous efficiency and/or the luminous color of the high pressure discharge lamp in more favorable states.
A high pressure discharge lamp lighting device according to the thirteenth aspect of the present invention, comprising a high pressure discharge lamp according to any one of the first to eleventh aspects of the invention, and a lighting circuit which biases a high pressure discharge lamp, and which has a crest value of the starting voltage of 15 kVp-p or more.
For instance, in order to instant re-light the high pressure discharge lamp used for a mobile headlight, a starting voltage which crest value is 15 kVp-p or more is applied. However, the high pressure discharge lamp provided with a light-transmissive ceramic discharge vessel is weak to the thermal shock at a starting operation, and easy to be cracked. Although such a problem could be solved, its application was limited since it was subjected to many restrictions such as the size, or it had few margins for the design.
In a high pressure discharge lamp according to the eleventh aspect of the present invention, the thermal conduction among the electrode, the metal pipe and the light-transmissive discharge vessel are good, and it is hard to have temperature differences, so that the temperature during the operation of the lamp will relatively equal. Therefore, we have learned that the high pressure discharge lamp has high resistance over the thermal and electric shocks such as starting or blinking of the lamp. Such a result is acquired remarkably in a combination with a lighting circuit having the crest value of the starting voltage of 15 kVp-p or more.
In this aspect of the invention, the lighting circuit for the high pressure discharge lamp can adopt various type of known circuit systems. For example, a high frequency AC lighting circuit, a low frequency AC lighting circuit and a DC lighting circuit are available. Furthermore, it is allowed to use in combination an igniter for supplying a start pulse voltage to the high pressure discharge lamp.
The high frequency AC lighting circuit primarily includes an inverter and an inductor suitable for lighting fluorescent lamps like compact single based fluorescent lamps with a high frequency ranging not less than 20 kHz to 200 kHz. According to this type of high frequency lighting circuit, it is able to reduce the size of the lighting apparatus and also the weight of the lighting apparatus. Thus, this sort of lighting circuit is very favorable to general purpose high pressure discharge lamp.
The low frequency AC lighting circuit is a type of lighting by a rectangular wave AC which is obtained by chopping a DC current at a low frequency. The frequency is generally less than around 500 Hz. The low frequency AC lighting circuit is able to reduce a flux rise time by supplying a lamp power 3.5 times of the rated lamp power at a starting of the lamp. Thus it becomes easy to control the lighting circuit. Accordingly this sort of lighting circuit is very favorable to automobile headlights.
The DC lighting circuit is a type of lighting by a DC power regulated by a chopper. This DC lighting circuit is not only favorable to operate a high pressure discharge lamp having an electrode structured for a DC lighting, but also favorable to automobile headlights and general purpose lighting apparatus since it is easy to control high pressure discharge lamps and is able to reduce the size and weight of the lighting apparatus.
Here, if required, the DC lighting circuit can adopt a AC-DC changeable lighting circuit which drives the lamp by a DC system at a stating time or for a prescribed time after the starting time, and after that drives the lamp by an AC system.
A luminaire according to the fourteenth aspect of the invention, comprising a luminaire principal body, the high pressure discharge lamp according to any one of the first to twelfth aspects of the invention which is supported by the luminaire principal body, and a lighting circuit which biases a high pressure discharge lamp.
In the fourteenth aspect of the invention, the term xe2x80x9cluminairexe2x80x9d has a wide concept including any device for utilizing light radiated from the high pressure discharge lamp in one object or another. For instance, the luminaire is able to be adapted to a screw-base-mount type high pressure discharge lamp, a lighting apparatus, a mobile headlight, a light source for optical fibers, an image projecting device, an optic-chemical device, or a fingerprint discrimination device. The term xe2x80x9cluminaire principal bodyxe2x80x9d means a whole portion of the luminaire except the high pressure discharge lamp.
The term xe2x80x9cscrew-base-mount type high pressure discharge lampxe2x80x9d means the luminaire in which the high pressure discharge lamp and the stabilizer are merged together, and further provided with a screw-base for receiving power when coupled to a lamp socket, so as to allow to be used in similar manner to the ordinary incandescent lamp. In case of constituting the screw-base-mount type high pressure discharge lamp, it is able to provide a reflector for condensing light so as that the high pressure discharge lamp presents desired light distribution characteristics. Furthermore, for moderately reducing the brightness of the high pressure discharge lamp, it is able to provide a light diffusing glove, or a cover. Further, it is able to use a screw-base having desirable specifications. Accordingly, for replacing directly with conventional light-source lamps, a screw-base the same as that of the conventional light-source lamps is able to be adopted.
When the luminaire is a lighting apparatus, it may be configured that the lighting apparatus is provided with the luminaire, and coupled to the high pressure discharge lamp, or it may be coupled to the high pressure discharge lamp when it is not provided with the lighting circuit. Further, When the lighting apparatus is provided with a luminaire, the luminaire may be located in the lighting apparatus or a place apart from the light apparatus such as a behind of ceilings.
The lighting circuit may be configured that the high pressure discharge lamp is lighted with any of the high frequency or low frequency. Further, it may not be provided with an rapid re-lighting function.